1. Field of the Invention
The present invention relates to a taper-etching method for forming a groove having a V-shaped cross section in a layer to be etched that is made of a dielectric material, and to a method of manufacturing a near-field light generator using the taper-etching method.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider that flies slightly above the surface of the magnetic recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To solve the foregoing problems, there has been proposed a technology so-called thermally-assisted magnetic recording. The technology uses a recording medium having high coercivity. When writing data, a write magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to use a plasmon generator, which is a piece of metal that generates near-field light from plasmons excited by irradiation with laser light. The laser light to be used for generating the near-field light is typically guided through a waveguide, which is provided in the slider, to the plasmon generator disposed near a medium facing surface of the slider.
U.S. Patent Application Publication No. 2010/0290323 A1 discloses a technology for coupling the light that propagates through the waveguide with the plasmon generator in surface plasmon mode via a buffer part, thereby exciting surface plasmons on the plasmon generator.
Here, a description will be given of an example of the shape of the plasmon generator and the arrangement of the plasmon generator and the waveguide. In this example, the plasmon generator is disposed above the top surface of the core of the waveguide. The plasmon generator has an edge part facing the top surface of the core of the waveguide. A cladding is disposed around the core. The cladding includes a portion lying between the edge part of the plasmon generator and the top surface of the core, and this portion of the cladding serves as the buffer part.
In the aforementioned plasmon generator, an end of the edge part located in the medium facing surface serves as a near-field light generating part. In the plasmon generator, the light that propagates through the core is totally reflected at the top surface of the core. This causes evanescent light to occur from the top surface of the core. Then, at least on the edge part of the plasmon generator, surface plasmons are excited through coupling with the aforementioned evanescent light. The surface plasmons propagate along the edge part to reach the near-field light generating part, and near-field light is generated from the near-field light generating part based on the surface plasmons. Such a configuration allows the surface plasmons excited on the plasmon generator to propagate to the near-field light generating part with high efficiency.
The aforementioned configuration can be formed in the following manner. First, a layer to be etched is formed using a dielectric material that is to be employed for the cladding. Part of the layer to be etched is located on the top surface of the core. Then, a groove that is V-shaped in cross section parallel to the medium facing surface (hereinafter, also referred to as V-shaped groove) is formed in the layer to be etched. This groove is formed not to reach the top surface of the core. Being provided with the groove, the layer to be etched becomes part of the cladding. The plasmon generator is then formed in the groove.
In the aforementioned configuration, the V-shaped groove has two wall faces that intersect at a predetermined angle, and the plasmon generator has two slopes that are opposed to the two wall faces. The two slopes of the plasmon generator intersect each other to form the edge part of the plasmon generator. The angle between the two slopes affects the intensity of surface plasmons excited on the plasmon generator and the spot diameter of the near-field light generated from the near-field light generating part. As the angle between the two slopes decreases, the edge part becomes sharper and the near-field light generated from the near-field light generating part decreases in spot diameter. To increase the intensity of the surface plasmons excited on the plasmon generator, however, the angle between the two slopes is preferably increased to some extent. This means that there is a preferred range for the angle between the two slopes. By way of example, the angle between the two slopes preferably falls within the range of 50° to 120°. The angle between the two slopes can be defined within the range of 50° to 120° by allowing each of the two wall faces of the V-shaped groove to form an angle (hereinafter referred to as inclination angle) in the range of 25° to 60° with respect to the direction perpendicular to the top surface of the layer to be etched, so that the angle between the two wall faces fall within the range of 50° to 120°.
A method for forming a V-shaped groove in a layer to be etched that will later become part of the cladding is to taper-etch the layer to be etched by employing reactive ion etching (hereinafter, also referred to as RIE). Generally in this method, an etching gas that contains a main component gas contributing to the etching of the layer to be etched and a gas for forming a sidewall protective film is used to taper-etch the layer to be etched. The V-shaped groove is formed by allowing the sidewall protective film to get deposited on the sidewalls of the groove being etched. The sidewall protective film is formed of a reaction product produced during the etching. The inclination angle of each of the two wall faces of the V-shaped groove depends on the ratio of the deposition rate of the sidewall protective film to the etching rate of the layer to be etched.
The aforementioned taper-etching by RIE gradually increases the depth of the groove being etched and gradually decreases the distance between the two sidewalls at the bottom of the groove. In general, as the depth of the groove being etched increases and the distance between the two sidewalls at the bottom of the groove decreases, in the region near the bottom of the groove the etching becomes predominant over the deposition of the sidewall protective film. Accordingly, for a V-shaped groove that is formed by taper-etching employing the conventional RIE, the inclination angle of each of the two wall faces decreases with increasing proximity to the lower end of the groove. As such, it has been difficult with the taper-etching by the conventional RIE to form a V-shaped groove having two wall faces that each form a constant or almost constant inclination angle from the opening to lower end of the groove.